An antenna assembly including an antenna reflector steering mechanism is disclosed. A reflector steering structure for adjusting the horizontal azimuth of a reflector includes a drive motor disposed on the rear surface of the reflector, a planet gear rotated by the drive motor, and a sectorial rack gear engaged with the planet gear and fixed to a support shaft, thereby achieving a compact design of an entire antenna structure. Further, by applying a structure with enhanced electrical insulation to rolling and slide contact portions of the drive unit and a portion undergoing change in contact pressure, radio performance of the antenna system may be prevented from changing according to steering of the reflector.